Seven people have died or been critically injured in what police are calling a "dark week" on South Island roads.

The three days of carnage come just as police issue a fresh warning about driving safety, announcing a summer speed tolerance of 4kmh above the speed limit.

FATAL TAI TAPU CRASH

In the latest incident, Lindsay Clive Sarchet has died in hospital overnight after a high speed crash in Tai Tapu.

Police said it appeared the 63-year-old man had lost control tried to overtake a car on Tai Tapu Rd, between Leadleys and Hayes road, at 2.30pm yesterday.

His car left the road, hitting a power pole and a culvert bridge.

Sarchet had to be cut from the vehicle, which came to a stop in a ditch. He was flown to hospital, but died in hospital overnight, police confirmed this morning.

Senior Constable Andy Williamson said Sarchet may have overtaken a number of other cars before the crash. Police were investigating how fast he was traveling at the time, but confirmed it was "a high speed crash".

TWO MOTORCYCLE CRASH FATALITIES NEAR HAAST

Two hours earlier, a trike rider was killed on the West Coast - the second motorcycle-related death on a stretch of highway near Haast this week.

The 55-year-old man was found dead at the scene of the crash, which happened about 12.30pm on State Highway 6, south of Haast.

No other vehicles were involved.

On Monday, Christchurch motorcyclist Steve Nottingham, 59, died after the trailer attached to his Harley Davidson clipped an oncoming campervan.

He was riding with his brother, Brent, who was in front when the crash happened about 1pm.

HEAD-ON CRASH AT BANKSIDE

The same day, two drivers were killed and their two female passengers were seriously injured after a head-on crash on SH1 at Bankside, just north of the Rakaia River. The dead were named yesterday as Indian man Gaurav Bhabhera, 28, and Ashburton woman Marae Judy Dean, 52.

Bhabhera's wife, Jaina Bhabhera, is still in a critical condition in hospital.

National road policing manager Superintendent Carey Griffiths said of the accidents: "This just makes us more resolved to do it [the summer speed crackdown].

"It's extremely unfortunate. It's a dark week on the roads for the families of the people involved."

The national road toll was at 226 yesterday. This time last year it was 268.

The police summer speed tolerance campaign runs from December 1 to January 31.